How to remove unwanted sounds and background music from a vocal sample

When you are looking for vocal samples to use in your industrial/trance/whatever electronic music, more often than not the sample will have unwanted background sounds or music. There is a simple process I use for removing those sounds. I use Logic on Mac OS X for my audio production, however I’m sure my technique can be adapted using different software if you are so inclined.

First, you will need to work with the original 5 channel audio, so that means ripping from a DVD. If the TV show or movie is not available in 5 channel audio then unfortunately this technique won’t work. Fortunately this is a rare problem unless you are sampling something really old. For this silly example we will use a clip of Tuvok in a battle situation on Star Trek Voyager.

Here is the original audio downmixed to stereo. As you can hear, there is a lot going on.

The next thing you will need to do is figure out which VOB file contains the section of audio with your sample and then strip the individual channels out of the AC3 audio. I use a program called a52decX which can be found here.

The vocals will be in the center channel, but usually the music and other sound effects will also be in this channel, albeit quieter. This is the center channel by itself. Often times the extra sounds are quiet enough you can just use it as is, especially if your song has lot of layers playing over it, but in this example it’s not much better than the downmixed stereo version. The left-front and right-front channels should contain the unwanted sounds and music, and we are going to use those two channels to cancel out the sounds in the center channel.

Create a new project in Logic with at least 3 audio tracks. We will be working in mono since the vocals are mono. Now add the left-front, right-front and center channels each to their own audio track. Create a bus object and set the output of both the LF and RF tracks to the bus. Set the bus output to Output 1-2 along with the center track. Set the locators roughly around the section with the sample.

Now here’s the key… put a Gain plugin (under Utility) on the bus and turn on Phase Invert. Remember, make sure all your tracks and objects are in mono mode. Play it and see how it sounds.

Because the sounds in the center channel are going to be a different volume than in the left and right front channels, it will probably not sound right… in fact it may not sound any better, or it may sound worse. The trick here is to manually adjust the gain on the plugin until it is cancelling the unwanted sounds as much as possible. It will most likely be impossible to remove them completely, but usually you can get them so quiet they will be impossible to hear in the final mix as long as there is some kind of ambient sound playing alongside it. In this example the best setting turned out to be a gain of -4.8.